Performance Of Solar Air Heater Research Articles

Effect of roughness width ratio in discrete Multi v-shaped rib roughness on thermo-hydraulic performance of solar air heater

The artificial roughness on underside of heated surface has been found to be effective technique to improve thermo hydraulic performance of solar air heater duct. In progression to the previous researches, the present study discloses the effect of discrete Multi v-rib on heat transfer and friction in a flow through artificially roughened solar air heater duct. The experimentations were performed to collect the data on heat transfer and friction by varying the Reynolds number (Re) between 2,000 and 20,000, relative width ratio (W/w) from 1 to 10, for the fixed values of relative gap distance Gd/Lv = 0.69, relative gap width g/e = 1.0, relative roughness pitch P/e = 8, relative roughness height e/D = 0.043 and angle of attack α = 60°. The present roughness geometry with relative width ratio (W/w) of 6.0 corresponding to flow Re of 20,000 yields the best thermo hydraulic performance.

Development of an Empirical Model for Assessment of Solar Air Heater Performance

ABSTRACTSolar flat plate collectors are used for meeting the hot air requirement in a number of applications ranging from domestic to industrial sectors. However, the varying degree of uncertainties of available solar radiation along with varying weather conditions often acts as restriction to their wider use. The varying input conditions like solar radiation, ambient temperature and relative humidity have diverse effect on the output of the flat plat collector used for hot air generation and poses difficulty in terms of reliability in providing the output as per users' requirement. This study refers to a method of predicting the output of flat plate collectors under varying working conditions. The model suggested here defines a relationship between the output in terms of instantaneous efficiency and the inputs, namely, solar radiation, ambient temperature, fluid inlet temperature and the mass flow rate. The relationship is based on the behavior of a given flat plate collector under certain sets of input ...

A review of thermohydraulic performance of artificially roughened solar air heaters

Abstract Solar air heaters form the major component of solar energy utilization system which absorbs the incoming solar radiation, converting it into thermal energy at the absorbing surface, and transferring the energy to a fluid flowing through the collector. The efficiency of flat plate solar air heater has been found to be low because of low convective heat transfer coefficient between absorber plate and the flowing air which increases the absorber plate temperature, leading to higher heat losses to the environment resulting in low thermal efficiency of such collectors. Artificial roughness in the form of repeated ribs is the most effective and economic way of improving the thermal performance of solar air heater. This paper presents an extensive review on the research carried out on artificial roughened solar air heater ducts. The objective of this paper is to review various studies, carried out on thermal as well as hydraulic performance of artificial roughened solar air heater ducts. The review presented in this paper will be useful for the researchers working in this area.

Exergetic performance evaluation of solar air heater having arc shape oriented protrusions as roughness element

Solar energy is a clean, abundant and easily available source of energy. Thermal performance of solar air heater does not take into account the energy loss due to friction for propelling air through the duct. In this work an attempt has been made to evaluate exergetic efficiency of roughened solar air heater duct provided with protrusions arranged in arc fashion over the absorber plate. The exergetic efficiency of a solar air heater was calculated analytically using developed correlations and the results were compared with that of a smooth flat-plate solar air heater. Design plots were also prepared in order to facilitate the designer for designing such type of roughened solar air heater within the investigated range of system and operating parameters.

Performance studies on flat plate solar air heater subjected to various flow patterns

The performance of flat plate solar air heater subjected to various flow patterns (over flow, under flow and double pass) were experimentally investigated. An aluminium flat plate of 1.2. × 0.7 m2 size was employed as absorber plate. Two glass plates of similar size were used as protection for heat loss from absorber plate to atmosphere. Performance of the solar air heater at various mass flow rates (0.014, 0.0279 and 0.042 kg/s) was also reported. Thermal efficiency is recorded higher during double pass experimental conditions. Heat gained by air is found higher at experimental conditions having double pass when compared with over flow and under flow.

Thermal and Thermo-hydraulic Performance of Packed Bed Solar Air Heater

Modification of flow passage of air in a solar air heater using a packing material is one of available techniques to considerably improve thermal performance of solar air heaters. In an outdoor experimental study, thermal and thermohydraulic performance of a packed bed solar air heater were evaluated and compared with that of a conventional solar air heater. It was observed that due to presence of mild steel chips in the flow passage of air in packed bed solar air heater, its thermal efficiency improved considerably as compared to that of conventional solar air heater for the entire range of Reynolds number considered in the investigation. Thermo-hydraulic performance of packed bed solar air heater was found to be better than that of conventional solar air heater for most of the Reynolds number range considered. However, beyond Reynolds number of 15000, conventional solar air heater outperformed packed bed solar air heater in terms of effective efficiency.

The Performance of Solar Air Heater with High Density Polyethylene Paper as Top Cover and Brown Sand Layer as an Absorber

Experimental investigations on the performance of a flat plate solar air heater (SAH) with brown sand as absorber and clear HDPE paper as top cover was done. The efficiency, heat gain factor and heat loss coefficient were determined for the collector. The effects of air mass flow rate and thermal efficiency was also studied. The SAH model was placed outdoors and tests were conducted in an open field between 0900 and 1500 Hrs. and parameters including solar radiation, temperature and air mass flow rates were recorded after every 20 minutes for 100 hours. Results show that, the efficiency increase with increasing air mass flow rate. The highest efficiency obtained was 54% at air mass flow rate of 1.22xl0 -5 Kg/s. The temperature difference between the outlet flow and the ambient reduces as the air mass flow rate increases with a maximum difference of 31°C at air mass flow rate of 6.83X10 -6 Kg/s which occurred at 1240 Hrs.

Plate Temperature and Heat Transfer Characteristics of Artificially Roughened Solar Air Heater

Higher value of intensity of radiation on absorber plate of solar air heaters and effective heat removal from the plate by the carrier fluid, air, enhances thermal performance of solar air heaters. The paper deals with the experimental results of enhancing the intensity of radiation by means of booster mirrors and that of heat transfer by means of providing artificial roughness on the air flow side of the absorber plate. An enhancement in radiation of about 40% have been found over the normal incident radiation by means of booster mirrors leading to higher rate of heat collection. The thermal performance parameters FR and F’ have been found to increase in the range of 90% to 130% and 92% to 135% respectively in comparison to those of smooth solar air heaters without booster mirrors and in the range of 10% to 15% in comparison to roughened solar air heater without booster mirrors for the same pressure drop due to artificial roughness within the range of the parameters investigated.

Effect of roughness height ratio in V down perforated baffle roughness on thermohydraulic performance of solar air heater: an experimental study

A substantial improvement in the thermal performance of solar air heater is found by using roughness on the underside of the absorber plate. In the present investigation, the effect of relative roughness height of roughness element on the thermohydraulic performance of solar air heaters is carried out. The range of roughness and flow parameters for the investigation are relative roughness height (e/H): 0.285–0.6, relative roughness pitch (P/e): 2, angle of attack (α): 60°, open area ratio (β): 12% and Reynolds number (Re): 3800–19,000. The relative roughness height of 0.285 is thermohydraulically better in comparison to other relative roughness heights. The results show that the V down perforated baffles is thermohydraulically better than the solid baffles.

Double Pass Solar Air Heater with Transvers Fins and without Absorber Plate

The single pass solar air heater, with transverse fins and wire mesh used as an absorber plate, is constructed and tested for thermal efficiency at a geographic location of Cyprus in the city of Famagusta. The absorber plate was replaced by sixteen steel wire mesh layers, 0.18 x 0.18cm in cross section opening and a 0.02cm in diameter. The fins were painted with black color and positioned transversely along the bed such that four equally spaced sections were created. The transversely fins are arranged in a way to force the air to flow through the bed like eight letter path. The obtained results show that for air mass flow rate rang between 0.011-0.032 kg/s, the thermal efficiency increases with increasing the air mass flow. The maximum efficiency obtained is 58% for the mass flow rate of 0.037 kg/s. Moreover, the temperature difference between the outlet flow and the ambient, ΔT, reduces as the air mass flow rate increases. The maximum difference between the outlet and ambient temperature obtained was 40.6 o C for mass flow rate of 0.011kg/s. Comparison with a conventional single pass collector shows a substantially enhancement in the thermal efficiency. INTRODUCTION: Heating air with solar energy is much cleaner than heating with fossil fuel, the delivered heat from air solar device can be used for drying agricultural products such as crop, grains, seeds, fruits, and vegetables. Solar air heaters are also used as pre heaters in industries and as auxiliary heaters in building to save energy during winter times [1]. Conventional solar air heaters mainly consist of panels, insulated hot air ducts and air blowers in active systems. The panel consists of an absorber plate and a transparent cover. There are many different parameters affecting on the solar air heater efficiency, e.g. collector length, collector depth, type of absorber plate, glass cover plate, wind speed, etc. [2]. The absorber plate area and heat transfer coefficient between the air and the absorber plate are two important parameters affecting the efficiency of the collector. When increased these parameters will increase the collector efficiency. On the other hand it will increase the pressure drops inside the solar air heater and increases the pumping power required [2]. The convective heat transfer rate between air flow and absorber plate could be augmented by increasing the absorber surface area and by increasing turbulence inside the bed [3]. The use of Vgroove absorber was found to be more efficient by 12% than the flat plate collector of similar design [4] [5]. Using corrugated plates is a suitable method to increase the thermal performance and provides higher compactness [6]. A mathematical model that allows the determination of the thermal performances of the single-pass solar air collector with offset rectangular plate fin absorber plate is developed by [7]. Experimental and theoretical investigations are carried out on sheet metal absorber in the form of a chevron pattern [8]. The effect of using absorber plates coated with various selective coating materials on the heater performance was also investigated by [9]. Comparisons were made among four types of solar air collectors by Suleyman [10]. It has been found that the performance of a solar air heating system can be improved by operating several sub collectors in series in place of a single large collector with the same total area [11] [12]. The study concludes that the performance of solar air heater with single plastic glazing and flat plate absorber were approximately 9% more than the collector with double plastic glazing. Another study was carried out to determine the comparative performance of one-pass for fixed and free fins,

Heat transfer enhancement in solar air heater with V-shaped perforated baffles

This experimental study, investigates the heat transfer and friction characteristics in a rectangular duct having its one broad wall heated and roughened with periodic V-down shaped perforated baffles. This work covered a range of Reynolds number (Re) 3800–19 000, open area ratio (β) 12%–44%, relative hole position (l/e) 0.429–0.571 for the fixed values of relative baffle height (e/H) 0.4, relative roughness pitch (p/e) 5, and angle of attack of 60°. The effects of relative hole position on Nusselt number and friction factor have been discussed and results compared under similar flow and boundary conditions to investigate the enhancement in Nusselt number and friction factor. The maximum enhancement in Nusselt number and friction factor has been obtained at an open area ratio of 12% and is of the order of 2.2 and 5.2 times of that of smooth duct, respectively. Thermohydraulic performance of solar air heater has been found to be substantially improved by the application such perforated baffles.

Analytical models of thermal performance of solar air heaters of double-parallel flow and double-pass counter flow

The development of two analytical models that describe the thermal behaviour of solar air heaters of double-parallel flow and double-pass counter flow is presented. Based on the local energy balances, algebraic expressions for the efficiency factor F′ and the overall heat loss coefficient, UL, as well as air temperature distributions along the collectors were obtained. In addition, the expressions of the mean temperatures of the two air streams and of the absorber plate were determined. The model corresponding to the solar collector with double-parallel flow predicts that the mass flow of air flowing between the absorber plate and the transparent cover is greater than the mass flow circulating through the other channel. The model corresponding to the solar collector of double-pass counter flow indicates that increasing the airflow proportionally increases the percentage temperature rise in the inlet channel. The analytical expressions developed are valuable tools that can be included in computational codes for the design and thermal analysis of solar air heating facilities or to improve current facilities. The paper include a graphic to estimate the heat transfer coefficients involved in energy balances.

Heat Transfer and Thermal Efficiency of Solar Air Heater Having Artificial Roughness: A Review

Artificial roughness applied on the absorber plate is the most efficient method to improve thermal performance of solar air heaters .Experimental investigations appropriate to distinct roughness geometries shows that the enhancement in heat transfer is accompanied by considerable rise in pumping power. In view of the fact, a designer needs to carefully examine shape and orientation of roughness elements in order to choose the best fit roughness geometry for intended application. In this paper some distinguished roughness geometry has been compared on the basis of heat transfer enhancement and thermo hydraulic performance. The objective of this paper is to review various studies, in which different artificial roughness elements are used to enhance the heat transfer rate with little penalty of friction. Correlations developed by various researchers with the help of experimental results for heat transfer and friction factor for solar air heater ducts by taking different roughened surfaces geometries are given in tabular form. These correlations are used to predict the thermo hydraulic performance of solar air heaters having roughened ducts.

A review of various approaches to optimize the solar air heater

A comparative study of various approaches to optimise and increase the performance of solar air heater is carried out in the present work. Various types of artificial roughness geometries in the absorber plate of solar air heater duct and their characteristics have been investigated for the heat transfer improvement or enhance the performance by many researchers. However, exergy data are more practical and realistic in comparison with the respective energy values that have been found in this communication.

Thermal and thermohydraulic performance of roughened solar air heater having protruded absorber plate

Thermal performance of solar air heater does not take into account energy loss due to friction for propelling air through the duct. Therefore, it is necessary to evaluate thermohydraulic performance in order to investigate simultaneous effect of thermal and hydraulic characteristics on performance of solar air heater. In the present paper thermal and thermohydraulic performance of smooth as well as roughened solar air heater has been investigated with the help of a mathematical model. Absorber plate of solar air heater has been roughened with the formation of protrusions. Optimum value of each roughness geometry parameter has been obtained on the basis of thermal and effective efficiency of roughened solar air heater. Design plots have also been prepared in order to facilitate the designer for designing such type of roughened solar air heater within the investigated range of system and operating parameters.

Performance improvement of a double-pass solar air heater with fins and baffles under recycling operation

The performance of a solar air heater featured with double-pass as well as fins and baffles design was investigated for the effect of recycling operation via both experimental and theoretical approaches. The experimental results deviate by 1.5–23% from the theoretical predictions. The performance of solar air heaters with different designs are compared, including the single-pass, double-pass with recycle, fined double-pass with recycle, and fined plus baffled double-pass with recycle. The double-pass device introduced in this study was proposed for aiming to strengthen the convective heat transfer coefficient and enlarge the heat transfer area. Based on both theoretical and experimental results, the collector efficiency of the fined plus baffled double-pass with recycle design is much higher than the other designs under different reflux ratios and mass flow rates. The optimal reflux ratio for the fined plus baffled double-pass design is about 0.5 while considering both the collector efficiency and the pumping power requirement. An economic consideration in terms of the heat transfer efficiency and power consumption increment for double-pass operation is delineated.

A Comprehensive Review on Roughness Geometries and Investigation Techniques Used in Artificially Roughened Solar Air Heaters

Artificial roughness applied on the absorber plate is the most acclaimed method to improve thermal performance of solar air heaters at the cost of low to moderate friction penalty. Experimental investigations pertinent to distinct roughness geometries unfolds that the enhancement in heat transfer is accompanied by considerable rise in pumping power. In view of the fact, a designer needs to carefully examine shape and orientation of roughness elements in order to choose the best fit roughness geometry for intended application. Moreover it is required to understand how flow field is affected by particular roughness geometry so that direction of future researches could be conceived. So as to elucidate the useful findings an attempt has been made to review roughness geometries employed in solar air heaters. Some distinguished roughness geometries have been compared on the basis of heat transfer enhancements and thermohaydraulic performance to draw attention towards their usefulness for specific applications. Furthermore, light is thrown on different investigation techniques adopted for prediction of heat transfer and friction characteristics of artificially roughened solar air heaters to recognize features and limitations of each technique.

Heat transfer and friction characteristics of solar air heater duct roughened by broken V-shape ribs combined with staggered rib piece

Thermal performance of solar air heater has been found to be substantially improved by the application of artificial roughness provided on underside of absorber surface. The present investigation was taken up to study the effect of broken V-rib roughness combined with staggered ribs on heat transfer and friction in a flow through artificially roughened solar air heater duct. This work covered a range of Reynolds number (Re) 3000–17 000, relative staggered rib pitch (p′/p) 0.2–0.8, relative staggered rib size (r/e) 1–2.5, relative gap position (s′/s) 0.2–0.8 for the fixed values of relative roughness pitch (p/e) of 10, relative roughness height (e/Dh) of 0.043, relative gap size (g/e) of 1, and angle of attack (α) of 60°. Experimental data pertinent to heat transfer and friction was generated and thermohydraulic performance was determined for different sets of roughness and flow parameters.

Optimization of a smooth flat plate solar air heater using stochastic iterative perturbation technique

► This research work proposes an algorithm based upon stochastic iterative perturbation technique . ► It predicts the set of optimized design and operating parameters of SFPSAH for maximum thermal performance. ► Effect of design and operating parameters on thermal performance of SFPSAH is adjudged quite satisfactorily. ► The results calculated from SIPT are compared with GA and RSGO and took less computational time. Due to low heat transfer capability, the thermal efficiency of solar collectors is very low and various techniques are implemented to increase the performance of solar air heaters. There is a need for optimization of design and operating parameters for maximizing the thermal gain from the solar air heating systems. In this paper a stochastic iterative perturbation technique (SIPT) is implemented to obtain the optimized set of different system and operating parameters i.e. the number of glass cover plate, emissivity of the plate, mean plate temperature, rise in temperature, tilt angle and solar radiation intensity for different Reynolds number. The results obtained have also been compared with the results obtained from genetic algorithm and random search global optimization technique for smooth flat plate solar air heater.

Performance analysis of W-shaped rib roughened solar air heater

Artificial rib roughness is a convenient method for enhancing thermal performance of solar air heater. An experimental investigation has been carried out to study the thermo-hydraulic performance of solar air heater using W-shaped ribs on absorber plate, the roughened wall being heated while the remaining three walls being insulated. W-shaped ribs have been tested both pointing downstream (W-down) and upstream (W-up) to the flow. The roughened wall has relative roughness height (e/Dh) of 0.03375, relative roughness pitch (p/e) of 10 and duct aspect ratio (B/H) of 8. The airflow rate corresponds to Reynolds number between 2300 and 14 000. The heat transfer results have been compared with those for smooth duct under similar flow and thermal boundary condition. Thermo-hydraulic performance ratio of roughened absorber plate by providing W-shape roughness is in the range of 1.46–1.95 for W-down and 1.21–1.73 for W-up ribs. Friction factor and heat transfer coefficient correlations have been developed based on the law of wall similarity and heat-momentum transfer analogy.